1. Field of the Invention
The present invention relates to a pattern evaluation method, a pattern matching method and a program.
2. Related Background Art
In various industrial fields, there has been widespread adoption of a method of evaluation using, as an index, a difference between the shape of a pattern which is an evaluation target (hereinafter referred to as a pattern to be evaluated) and a reference figure thereof. For example, for the evaluation of a semiconductor device pattern, a scanning electron microscope (SEM) image as an inspection image of the pattern and computer aided design (CAD) data as design data for the SEM image are used to calculate the degree of similarity between a worked shape of the device pattern and a design shape thereof, thereby judging whether or not the pattern is good. One example of such a conventional evaluation method will be described below.
First, the edge of the pattern to be evaluated is detected from the SEM image which is the inspection image. Moreover, when a CAD figure is provided in a binary file such as GDSII as a design pattern, it is uncompressed as a binary image to likewise detect information on the edge of the design pattern.
Next, the SEM image is referred to the binary image to detect the positions of both the patterns. Specifically, the relative positions of both the patterns are gradually changed in a predetermined form, and the degree of difference or similarity at that moment is calculated every time, thereby detecting a position at which the calculated value becomes a maximum or minimum value. For the degree of similarity, the use is generally made of parameters such as a normalized correlation in which the brightness of the image are normalized, or a cross correlation. The edge of the SEM image is superposed on the CAD figure by the above-mentioned image matching.
Subsequently, one or several regions of interest (ROI) is/are set in the superposed patterns, and dimensions between the edges of both the patterns in the ROI are measured. One or several dimensional values thus obtained is/are referred to a separately defined standard to judge whether or not the pattern to be evaluated is acceptable.
However, the conventional technique described above has the following problems.
First, since the correctness of the superposition of the edge of the pattern to be evaluated on the CAD figure depends on the pattern shape, it has been difficult to make a comparison by the degree of coincidence between differently shaped patterns. Further, since it is necessary to sequentially execute image processing of two kinds including the image reference and the calculation of the degree of difference between patterns, there has been a problem of time-consuming calculation, which therefore increases costs for the pattern shape evaluation. In addition, there is no clear standard for a threshold value used for the image matching, and the threshold value is set in dependence upon the experience of an operator under the present circumstances.
Furthermore, in the conventional technique described above, the shape of the pattern is evaluated with several dimensional values, so that there has been a problem that a large number of ROIs have to be set to evaluate a complicated pattern and much effort is needed for the calculation to analyze a large amount of dimensional data thus obtained.